For manual customization log messages you need to create your own LogRoute class. In your situation you need inherit class from CFileLogRoute and override method formatLogMessage (such in example):
class MyFileLogRoute extends CFileLogRoute{
protected function formatLogMessage($message,$level,$category,$time)
{
//enter code here your custom message format
return @date('Y/m/d H:i:s',$time)." [$level] [$category] $message\n";
}
}
Than configure your configuration file:
'log' => array(
'class' => 'CLogRouter',
'routes' => array(
array(
'class' => 'MyFileLogRoute',
'levels' => 'error, warning, info',
'categories' => 'application.*',
'logPath' => dirname(__FILE__).'/../../../../../logs/',
),
...
And yes, @ragingprodigy is right: you can set define('YII_DEBUG', 0) or define('YII_TRACE_LEVEL', 0) in index.php to remove stack trace from log messages
defined('YII_TRACE_LEVEL') or define('YII_TRACE_LEVEL',3);in yourindex.phpfile